Undead

These creatures, having no memory of their lives before, are simple, and wish only to fulfill their basic needs without recognizing any other function, purpose, or person. The aggression these creatures have is theorized to be two things:

One, is that their mental and emotional stunting causes immense frustration in the creatures that were once alive and had higher function.

Two; these creatures are actually acting as predators towards the living, and are attempting to fulfill the basic needs they had when alive, however, without previous morals or sense of self-preservation, they go after taboo and dangerous prey (thus explaining the "feeding" behavior found in most zombies.)

"In a way it is almost like a loose pathogen that can reanimate the dead, but instead of anything like disease, it's an ethereal force."

This disease can be "cured" by removing the magic from these reanimated corpses, which, in its simplest terms, is just blessing the creature to death.